Clockwork Orange Planet

This month marks the one-year anniversary for both the Spirit and Opportunity Mars rovers. Spirit landed on Mars on January 3, 2004, and Opportunity arrived 3 weeks later, on January 24.

Since the rovers were designed to last for just three months, they have far exceeded the expectations of even the most optimistic mission planners. So far, Spirit has driven over 4 kilometers. Opportunity has driven half that distance, partly because it landed right in a crater on arrival, stunning scientists with their first view of martian bedrock layering.

Spirit is currently exploring the Columbia Hills within the Gusev Crater, and recently found a new type of rock. Named "Wishstone," the rock is composed of grains of various sizes, and is thought to be the result of a volcanic explosion or impact event. For reasons the scientists do not yet understand, the rock is much richer in phosphorus than any other rocks seen so far on Mars.

"One possibility is that the explosive event – the igneous rock itself – was rich in phosphorus to start with," says Steve Squyres, principal investigator for the rover science payloads. "The other possibility is it’s a phosphate that was deposited with water."

Water-deposited phosphorus would suggest a different type of water chemistry than what occurred just 500 meters away, where the rocks are rich in chlorine, sulfur, and bromine. Scientists expect that Spirit will be investigating more such rocks as it climbs Husband Hill, heading for the summit.

Meanwhile, Opportunity spent some time sniffing around its discarded heat shield. This shield protected the rover during its descent through the martian atmosphere, and then detached before the rover’s airbags inflated. When the heat shield hit the ground, it split in two and turned inside out.

By looking at the heat shield with a microscopic imager, engineers hope to determine how deeply the atmospheric friction charred the shield’s protective layers.

"For the scientists, this has been really fun, because we get to sit back and let all the engineers do all the really hard thinking," says Squyres. "We just take pictures to make the engineers happy."

Opportunity also spotted a pitted meteorite the size of a basketball near the heat shield. While most meteorites on Earth are rocky, the meteorite on Mars is metal-rich, composed of mostly iron and nickel.

"We’ve been seeing lots of cobbles out on the plains, and this raises the possibility that some of them may in fact be meteorites," says Squyres. "We may be investigating some of those in coming weeks."

Opportunity’s future plans also include a drive south toward a region called the "etched terrain." Small craters dot the landscape along the way, and the rover will move from crater to crater, eventually reaching an unusual circular feature called "Vostok."

Firouz Naderi, manager of the Mars Exploration program at the Jet Propulsion Laboratory, says that more Mars discoveries are on the way.

"The opportunity to go to Mars comes around like clockwork, every 26 months," says Naderi. "So at any given time, we have some assets on or above Mars, some that are fixing to go, some on the drawing board, and some that are still being cooked up as a concept in the minds of some pretty smart people."

"All of the (missions) are aimed at answering two fundamental questions," Naderi adds. "One is, was the environment on Mars ever right for the emergence of life? And second, if so, did life in fact emerge?"

Naderi says the current strategy for answering these questions is to have orbiters above Mars, looking for places that may have once had liquid water. The rovers are then sent in for a closer look. For instance, the Mars Global Surveyor detected hematite, a mineral that often forms in the presence of water. So the MER rovers were sent to places where hematite was plentiful and where landing wouldn’t be too difficult.

In the coming decade, scientists hope to bring a Mars sample back to Earth.

"We need to learn how to build upon these tremendous findings – these phosphatic rocks, these high sulfur rocks, these ancient habitable environments – by bringing those samples back here to Earth," says Jim Garvin, lead scientists for Mars exploration at NASA’s Headquarters in Washington, D.C. "Bringing (samples) back here (will) show us we can make the round trip before we send the women and men to hit the ultimate home run by being there on Mars."